Rotor blade tip section

ABSTRACT

A main rotor blade includes a tip section having a splice cap, a structural tip spar, a core and an upper and lower tip skin. The tip section is mounted to a central blade section by mounting the tip spar to a main blade spar. The tip spar includes a first surface substantially parallel to a second surface. The first and second surfaces each extend from a shear web therebetween to define the generally C-shape in cross section. The shear web generally carries rotor blade torsional loads and eliminates the heretofore required structural core. A section of the tip spar overlaps a section of the main blade spar. The tip section thereby transfers the loads carried thereby through interaction between the overlapped spar sections. The tip section core and skins need not be structural members as the tip spar carries rotor blade tip section torsional loads.

BACKGROUND OF THE INVENTION

The present invention relates to a rotary wing aircraft rotor blade, andmore particularly to a rotor blade tip spar arrangement.

Conventional rotary wing aircraft rotor blades often include a tipsection of a selected sweep, taper, and form to improve the bladeperformance. Anhedral tip sections increase hover performance and liftcapabilities of a rotary wing aircraft on which the blades are fittedwithout increasing the structural features of the main rotor hub andspindle.

The tip section of the main rotor blade is subjected to the greateststresses/strains due to aerodynamic forces, and concomitantlyexperiences the greatest structural degradation due to wear and abrasion(due to the high rotational velocity of the main rotor blade tip),during operation of the helicopter main rotor assembly. These forces areonly increased upon a tip section which utilizes an anhedral or othernon-straight form.

Disadvantageously, a tip section that utilizes a non-straight form maybe relatively difficult and expensive to manufacture. For example,current anhedral tip sections require numerous structural components tocarry the loads induced by the anhedral form. Current anhedral tipsections each require two structural anhedral tip skins and twostructural honecomb core pieces along with non-structural pieces andredundant fasteners. Structural components may cost five times that ofnon-structural components. Furthermore, structural components requiremultiple expensive manufacturing, and in some instances proprietary,processes to produce the anhedral tip sections.

Accordingly, it is desirable to provide an inexpensive rotor blade tipsection that is applicable to anhedral form, minimizes the number ofstructural components, yet avoids adversely affecting the load bearingcapabilities of the rotor blade.

SUMMARY OF THE INVENTION

The main rotor blade according to the present invention provides anon-straight tip section, which includes a splice cap, a tip spar, acore and an upper and lower non-structural tip skin. The core and skinsneed not be structural members as the tip spar carries rotor blade tipsection torsional loads. Relatively complex tip section forms thatutilize a minimum of structural components are readily achieved by thepresent invention.

The tip section is mounted to a central blade section by mounting thetip spar to a main blade spar. The tip spar includes a first surfacesubstantially parallel to a second surface. The first and secondsurfaces each extend from a shear web therebetween to define a generallyC-shape in cross section. The shear web generally carries rotor bladetorsional loads and eliminates the heretofore required structural core.A section of the tip spar overlaps a section of the main blade spar. Thetip section thereby transfers the loads carried thereby throughinteraction between the interaction of the overlapped spar sections.

The present invention therefore provides an inexpensive rotor blade tipsection that is applicable to anhedral form, minimizes the number ofstructural components, yet avoids adversely affecting the load bearingcapabilities of the rotor blade.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a top plan view of an exemplary main rotor blade assembly;

FIG. 2 is an expanded to plan view of a tip section of a rotor blade;

FIG. 3 is an expanded partial phantom perspective view of a tip sectionof a rotor blade;

FIG. 4 is a cross-sectional view of the main rotor blade of FIG. 3 takenalong line 3-3 thereof;

FIG. 5 is an exploded view of a tip section of a rotor blade;

FIG. 6 is an expanded partial phantom perspective view of an extendedtip section of a rotor blade; and

FIG. 7 is an exploded view of a tip section of a rotor blade illustratedin FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a general perspective view of a helicopter rotorsystem 10 which includes a hub assembly 12 to be driven for rotationabout an axis of rotation 13. A plurality of main rotor blade assemblies14 project substantially radially outward from the hub 12 and aresupported therefrom in conventional fashion by an attachment 15. Anynumber of blades 14 may be used with the rotor system 10. It should beunderstood that although a particular rotor system 10 is illustrated inthe disclosed embodiment, other attachments, flex beams, main and tailrotors will benefit from the present invention.

Each main rotor blade 14 includes a root section 16, a central section18 of aerodynamic shape, and a tip section 20, which culminates in ablade tip 22. The blade sections 16, 18, 20 cooperate with the hub 12 todefine a blade radius R between the axis of rotation 13 and the bladetip 22. A blade chord C extends between a blade leading edge 24 and ablade trailing edge 26.

The blade 14 is fabricated with a selectively shaped tip section whichincludes a selected combination of rearward sweep, taper, dihedral,width, and anhedral. The tip section 20 operates to unload the blade tip22, thereby producing a more uniform lift distribution throughout thespan of the blade and also producing a more uniform downwash effect, aswell as decreasing the power required to drive the rotor 10 and therebyincreasing lift and hover performance. The tip section preferablyreduces the intensity of the tip trailing edge vortex and also directsor displaces the tip trailing edge vortex so that it causes minimalinterference on the following blade. The rotor blade tip section 20preferably includes an anhedral form, however, other angled and nonangled forms such as cathedral, gull, bent, and others will benefit fromthe present invention.

Referring to FIG. 2, each blade 14 includes a main blade spar 30 whichextends from the root portion 16, through the central portion 18, andinto the tip section 20 preferably prior to an anhedral droop 32 (FIG.3). The main blade spar 30 is a structural member having high torsionaland axial stiffness and strength, and in the preferred embodiment ismade of a high strength composite material. However, the spar may alsobe made from a high strength metal, such as titanium. The blade 14extending from the root portion 16 and through the length of the centralportion 18 preferably include a core material covered by a compositeskin (illustrated schematically at 31; FIG. 3) which defines theaerodynamic shape of the blade as generally known.

Referring to FIG. 4, a sectional view of the tip section 20 isillustrated. The tip section 20 includes a splice cap 34, a tip spar 36,a core 38, and an upper and lower non-structural tip skin 40, 42 (alsoillustrated in an exploded format in FIG. 5). The tip spar 36 ispreferably the only structural component within the tip section 20.

The splice cap 34 is made of a wear-resistant material, such as nickelto provide abrasion protection for the tip section 20. The splice cap 34also provides control of airfoil tolerances of the tip section 22. Thesplice cap 34 preferably attaches to an open end 44 of the generallyC-shaped tip spar 36 and overlays the forward edges of the skins 42, 44.The splice cap 34 and tip spar 36 mount directly to the main rotor mainblade spar 30 (FIG. 3) to provide a rigid structure which supports theloads induced by the tip section 20 with a minimum of structuralcomponents. The splice cap 34 and tip spar 36 are preferably bonded tothe main rotor main blade spar 30 and additionally may include redundantfasteners. An adhesive material, such as epoxy film adhesive, is apreferred bonding agent.

The tip spar 36 preferably includes a first surface 46 substantiallyparallel to a second surface 48. The first and second surfaces 46, 48each extend from a shear web 50 therebetween to define the generallyC-shape in cross section. The shear web 50 generally carries rotor bladetorsional loads and eliminates the heretofore required structural core.

The first and second surfaces 46, 48 and shear web 50 need not be planarand need not be of consistent thickness. That is, a more rounded C-shapein cross section, a U-shape in cross section or other combinations ofshapes which generally mate with a main rotor spar will benefit from thepresent invention.

The tip spar 36 defines a first spar section 52 angled relative a secondspar section 54. That is, the first spar section 52 generally extendsalong an axis defined by the main rotor main blade spar 30 and thesecond section is angled relative thereto to define an anhedral form. Itshould be understood that the tip spar 36 may alternatively includemultiple sections angled relative to each other to define other tipsections such as a multi-angled cathedral tip section 20 a (FIGS. 6 and7). Relatively complex forms are readily achieved by the presentinvention.

Preferably, the tip spar 36 is manufactured from IM7 graphite materialin female mold, vacuum bagged and cured as generally known. The tip spar36 may then be NDI inspected as also generally known. It should beunderstood various manufacturing processes will also benefit from thepresent invention.

The tip section 20 is mounted to the central section 18 by mounting thetip spar 36 to the main blade spar 30. The tip spar 36 is mounted to themain blade spar 30 through bonding, however, other removable attachmentarrangements will also benefit from the present invention such that thetip section 20 is field replaceable.

Referring to FIG. 5, a section S1 of the tip spar 36 overlaps a sectionS₂ of the main blade spar 30. That is, sections S1, S2 fit in a malefemale relationship. Preferably, the center of the overlap is located atapproximately 91.5% R (FIG. 2). It should be understood that otheroverlap length and locations will also benefit from the presentinvention. The inner perimeter P1 of section S1 and the outer perimeterP2 of section S2 are preferably reduced such that a flush surface jointis formed therebetween (FIG. 4). It should be understood that otherinterfaces will also benefit from the present invention. The tip section20 thereby transfers the loads carried thereby through interactionbetween the interaction of the sections S1 and S2.

The core 38 is preferably a one-piece non-structural member as the tipspar 36 carries rotor blade tip section torsional loads. The core ispreferably a non-formed, low-density core piece of a three pound densitywhich replaces conventional multiple structural cores thereby reducingpart count and machining operations.

The upper and lower non-structural tip skin 40, 42 are preferablynon-structural skins such as a three ply fiberglass lay-up.Alternatively, the skins are formed using layers of graphite fiber andfiberglass fiber such that the skins include three layers of fiberglassfiber, and in the leading edge of the blade, where the blade is subjectto the greatest wear and tear, layers of graphite fiber are added tofurther enhance the strength and durability of the skin.

Referring to FIG. 6, another blade assembly 14A is illustrated. The tipspar 35A is of an extended length and includes an extended splice cap34A (FIG. 7), which forms the leading edge of both the tip section 20Aand intermediate section 18A. It should be understood that otherconfirmations which also essentially integrate the tip and intermediatesections 20, 18 will benefit from the present invention. That is, thepresent invention is applicable to sections of a rotor blade other thanjust the tip section.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The preferredembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

1. A tip section assembly for a rotor blade comprising: a tip sparsection substantially C-shaped in cross section.
 2. The tip sectionassembly as recited in claim 1, wherein said tip spar section mounts tomain blade spar.
 3. The tip section assembly as recited in claim 1,wherein said tip spar section comprises an open side which faces aleading edge of a main rotor blade.
 4. The tip section assembly asrecited in claim 1, wherein said tip spar section comprises a first tipspar section angled relative a second tip spar section.
 5. The tipsection assembly as recited in claim 1, wherein said tip spar sectiondefines an anhedral relative a main blade spar.
 6. The tip sectionassembly as recited in claim 1, further comprising a non-structural tipskin mounted to said tip spar section.
 7. The tip section assembly asrecited in claim 1, further comprising a splice cap mounted to an openside of said tip spar section.
 8. A tip section assembly for a rotorblade comprising: a structural tip spar section comprising a firstsurface substantially parallel to a second surface, said first surfaceand said second surface each extending from a shear web therebetween. 9.The tip section assembly as recited in claim 8, wherein said tip sparsection mounts to main rotor blade spar such that an open side betweensaid first planar section and said second planar section faces a leadingedge of a main rotor blade.
 10. The tip section assembly as recited inclaim 9, wherein said tip spar section defines an anhedral relative amain rotor blade spar.
 11. The tip section assembly as recited in claim9, wherein said tip spar section is at least partially out of a planedefined by a main rotor blade spar.
 12. The tip section assembly asrecited in claim 8, further comprising a non-structural tip skin mountedto said tip spar section.
 13. The tip section assembly as recited inclaim 12, wherein said tip skin is manufactured of a three-plyfiberglass lay-up.
 14. The tip section assembly as recited in claim 8,further comprising a splice cap mounted to an open side of said tip sparsection.
 15. The tip section assembly as recited in claim 8, whereinsaid first surface and said second surface are non-planar.
 16. The tipsection assembly as recited in claim 8, wherein said first surface, saidsecond surface and said shear web define a substantially C-shape incross section.
 17. The tip section assembly as recited in claim 8,wherein said first surface, said second surface and said shear webdefine a substantially U-shape in cross section.